Characterization and relative ionization efficiencies of end-functionalized polystyrenes by matrix-assisted laser desorption/ionization mass spectrometry

Abstract

The properties and relative ionization efficiencies of a series of polystyrenes (PS) with hydroxyl, hydrogen, tertiary amine, and quaternary amine end-functionalities were examined by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS). The hydrogen and hydroxyl functionalized PS ionized via attachment of a single Ag ϩ cation, as expected. However, tertiary amine PS oligomers were found in (M Ϫ H) ϩ and (M ϩ H) ϩ forms, in addition to M ϩ Ag ϩ , while the quaternary amine PS oligomers only ionized to the M ϩ form. Analysis of tertiary amine PS spectra revealed varying ratios of the three ionic forms depending on the oligomer length, pointing to a change in ionization efficiency. When the bulk samples were compared, the quaternary amine end-functionalized PS gave a ten-fold higher ionization efficiency over all others studied, likely because of the preexisting charge on the functionality. Samples with hydroxyl and hydrogen functionalities had similar ionization efficiencies, with the tertiary amine slightly higher, depending on the molecular weight. Changes in molecular weight affected the relative ionization efficiencies in varying fashion depending on the end functionality, though average molecular weight measurements were largely unaffected by end-functionality. Quantification of end-functionalized polystyrenes with different ionization efficiencies was found to be possible if due care was taken. (J Am Soc Mass Spectrom 2003, 14, 648 -657)

Quantitation of synthetic polymers using an internal standard by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

“…A more systemic study will be carried on later. The similar results of end-group influence on ionization efficiencies on polystyrenes have been reported by Johnston and coworkers [28].…”

The unexpected formation of [M − H]+species during MALDI and dopant-free APPI MS analysis of novel antineoplastic curcumin analogues

“…Awad et al [18][19][20][21][22] and APPI. [23] Most publications focused on three mechanisms to explain the [M À H] + formation: (1) loss of H 2 from the protonated analyte, (2) hydrogen atom transfer from the analyte radical cation or (3) + as a possible product ion via H 2 loss (data not shown).…”

“…[13] Based on the nature of the N-substituents, the curcumin analogues have been categorized into four groups: phosphoramidates, secondary amines, amides and mixed amines/ amides (Scheme 2). + ions was significantly reported with alkanes during chemical ionization (CI) [14,15] and APCI-MS. [3] Subsequently, [M À H] + ion formation has been detected with a wide range of compounds with various ionization techniques, such as ESI, [16,17] MALDI, [18][19][20][21][22] APPI, [23] desorption APPI, [24] desorption ESI [24] and direct analysis in real time. [25] Several mechanisms have been proposed to explain the formation of [M À H] + during MS-analysis that could be summarized into three main mechanisms: (1) loss of hydrogen molecule from the protonated [M + H] + ion, (2) hydrogen transfer from the analyte radical cation or (3) hydride abstraction from the neutral analyte molecule [14][15][16][17][18][19][20][21][22][23][26][27][28] (Scheme 4).…”

Liquid chromatographic–electrospray mass spectrometric determination of 1-methyl-4-phenylpyridine (MPP+) in discrete regions of murine brain

“…There is one explanation for the difference in sensitivity between MPP + and MPTP that may have a bearing on MPTP detectability. Cox et al (2003) have indicated that tertiary amine functionalities on polystyrene polymers have several modes of ionization available (M−H + , M+H + , M .+ ) in contrast to analogous quaternary amines which simply have M + when studied by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. This principle may account for the superior sensitivity of the system described here to MPP + (a quaternary amine) in contrast to that of MPTP (a tertiary amine).…”